1. Field of the Invention
The present invention relates to a load drive circuit that drives a load thereby controlling its output voltage.
2. Description of the Related Art
Drive circuits using a MOS-type output are known which control the drive of general electric apparatuses. In the drive circuits using a MOS-type output, protection is required with respect to the gate to source or drain to source withstand voltage of the output MOS transistors. For example, a protection circuit is known which is a series circuit of serially connected Zener diodes, connected between the gate and source of a MOS transistor for the over voltage protection. This type of protection circuit is described in Japanese Patent Application Kokai No. 2005-323489, (hereinafter called Reference 1).
The protection circuit described in Reference 1 comprises a MOSFET provided in between a battery and a load, and a series circuit having two Zener diodes serially connected between the gate and source of the MOSFET, and further having a transistor. When an over-current flows and thus the gate-to-source voltage of the MOSFET exceeds a reference voltage, the transistor is controlled to be ON, thereby clamping the gate-to-source voltage of the MOSFET to the Zener voltage of the Zener diode to decrease the drive capacity of the load drive circuit, and thus the over-current is reduced to achieve the gate-to-source over voltage protection.